Consumers' appetite for more performance and functionality from a small form factor, multi function computing device, such as a smart phone, a tablet computer, or a laptop notebook computer, typically outpaces developments in low power consumption electronics. Thus, manufacturers of such devices are forced to find better ways of coping with high temperature effects (thermals) while trying to maintain a desired performance level for the user. A given device may include more than one source of heat that individually, or in concert with others, causes a temperature of the device to rise above a desired maximum temperature. Furthermore, heat may come from outside of the device when, for example, the device is being used in a hot room or in direct sunlight. To resolve thermal issues, several proactive measures have been developed including reducing the speed or power supply voltage at which a constituent processor of the device is running, engaging cooling fans, lowering a cellular network RF transmit power limit, or dimming a display. Many devices designed today require these proactive measures to provide adequate performance in order to not frustrate the user's experience with the device, under various thermal conditions.
An example thermal arena to monitor and manage in a device is the device's external case temperature. This should be kept in a predefined range, e.g., as specified by Underwriters Laboratories (UL) for consumer grade cellular telephone handsets. During normal operation, the external case of the device should not become so warm as to become uncomfortable for the user to continuously touch during use, e.g., while it is being held in the user's hand or against the user's ear. The external case may be heated by any power consumed within the device, and the hottest points on the external case will most likely be in proximity to the component having the highest power dissipation. Such components include for instance an RF power amplifier (PA), that drives a cellular network RF communications antenna, and an applications processor, both in a mobile telephone or smart phone.